Demonstrated reliability of plastic-encapsulated microcircuits for missile applications

For the past decade, overall reliability improvement and product availability have enabled plastic encapsulated microcircuits (PEM) to move from consumer electronics beyond the relatively large and reliability-conscious automotive market, into the military market. Based on the analysis of the worst-case PEM scenario for military applications, demonstrating the moisture reliability under long-term (20 years) dormant storage environments has become the last hurdle for PEM. Studies have demonstrated that PEM can meet the typical missile environments in long-term storage. To further validate PEM reliability in missile applications, Texas Instruments (TI) conducted three separate studies involving 6 years of PEM moisture-life monitoring and assessment, testing of the standard PEM electrical characteristics under the military temperature ranges (-55°C to +125°C), and assessing their robustness in moisture environments after the assembly processes. These TI studies support the use of PEM in missile (or similar) applications. Effective focus on part and supplier selection, supplier teaming, and process monitoring is necessary to maintain the PEM reliability over the required environments at the lowest cost. This paper assesses PEM reliability for a selected missile storage environment using the industry-standard moisture testing, such as biased HAST or 85°C/85%RH (relative humidity), for demonstrating the PEM moisture survivability. The moisture reliability (MTTF) or average moisture lifetime of PEM is assessed to correlate PEM capability to anticipated field-performance environments